In most known photographic processing apparatus, photographic material is passed through a series of baths containing processing solutions appropriate to that particular material. The material is driven sequentially through the baths by roller pairs.
In other processing apparatus, a plurality of rollers is used to pick up processing solutions from trays and transfer the solutions on to the material as it is passed across the top of the rollers.
In both cases, the material is free and it is effectively passed from solution to solution. For example, in a simple photographic process, developer, fixer and wash solutions have to be arranged in order so that the material can pass from one processing stage to the next in one pass.
However, in the processing apparatus described above, there is no flexibility as it is not possible to return to a processing stage already visited.
Furthermore, it is difficult to reduce the size of the processing apparatus when several identical processing stages are required.